The present invention relates to torque-producing friction hinges. More specifically, the present invention relates to a clip or multiple clips radially compressed on a shaft to produce rotational friction or torque between the shaft and the clip(s).
Friction hinge devices are used to support objects at selected angular positions relative to a main body. For example, friction hinges are used in notebook computers to support a computer screen at various angular locations relative to a computer base. They are also used to support windshield visors in motor vehicles at various angles.
One type of friction hinge is a spring hinge which utilizes a helical spring wrapped around a shaft. In a relaxed state, the spring has an inner diameter less than the outer diameter of the shaft to frictionally engage the shaft so that the spring and shaft will tend to rotate together. In use, the shaft is connected to a rotatable body. As the body and the shaft are rotated, one of the spring ends or xe2x80x9ctoesxe2x80x9d is oriented to contact a stop, which is typically part of a stationary support. The engagement of the spring toe with the step will cause the spring to slip relative to the shaft, rather than rotate with the shaft. This will generate torque. Such a spring hinge can be designed to provide a fairly constant torque or resistance to rotation throughout its range of motion.
Another type of a friction hinge device is an axial compression hinge. An axial compression hinge includes at least two friction discs compressed against each other on a shaft. The axial compression hinge utilizes a compression force along the axis parallel with its shaft. An arm is attached to one of the friction discs while the other friction disc is secured to the shaft. As the arm is rotated relative to the shaft, the friction between the surfaces of the discs creates torque.
Both the spring hinge and the axial compression hinge have limitations and difficulties. For example, with respect to the axial compression hinge, it is often difficult to attach the friction discs to the arms and also difficult to secure the discs to the shaft. The difficulty in attaching the arms to the discs greatly increases when additional discs are added to the shaft in an attempt to increase torque. More particularly, each disc that is added must have an additional arm attached to it. The space limitations of most applications make the connection of additional arms impractical.
The axial compression hinge also must have a mechanism which sufficiently delivers enough axial compression force to maintain friction between the discs. It is often difficult to maintain a relatively constant axial compression force on the discs. This causes non-constant torque which is a very undesirable characteristic.
Also, the particular connection between the friction discs and the arm can affect the overall torque produced by the axial compression hinge. The friction effect is not constant or predictable and may also cause non-constant torque.
Finally, the friction discs must be formed to very specific tolerances. Variations in the size of the discs will significantly affect the overall torque of the device. This presents problems in machining multiple components to exact tolerances.
With respect to the spring hinge, the overall size of the spring hinge is often too large for certain applications requiring relatively large torque. With the spring hinge design, the most effect way to substantially increase torque is to add additional springs to the shaft. This will substantially increase the size of the package required to contain the friction spring hinge. Space limitations of many applications make the addition of spring elements impractical.
In addition, spring hinges require that the spring toe be secured to, or otherwise engage, the support base so that the spring is held stable as the shaft is rotated relative to the support base. However, if the spring toe is extended to engage a stop portion on the support base, this engagement will only occur in one direction of rotation of the shaft. In the opposite direction the spring toe will rise off the stop portion of the support base allowing the spring to rotate with the shaft. Hence, the torque producing effect of the spring hinge is unidirectional. Bi-directional spring hinges exist, but these usually require engaging a spring toe to the support base at both ends of the spring so that the spring is held stable as the shaft is rotated in either direction.
Spring hinges also require very accurate machine tolerances. The spring toes must terminate precisely at the stop portion of the support structure. The precise location of the spring toes relative to the stop is critical to the performance of the spring hinges. If the space between the spring toe and the stop is too large, the hinge will have free play, that is, there will be no torque for a limited range until the spring toe engages the stop. On the other hand, if the radial tolerance between the spring toe and the stop is too small, the toes will make the spring hover over the shaft resulting in no or low torque.
Finally, the overall torque of the spring hinge is usually significantly affected by the antirotation elements of the device. More specifically, the overall torque of the spring hinge is significantly affected by the engagement of the spring toe with the stop on the support base. As the spring toe engages the support base stop, the spring tends to xe2x80x9cwrap openxe2x80x9d, that is, lift off the shaft. This decreases the friction between the spring and the shaft, which in turns decreases the torque produced by the spring hinge.
The present invention solves these and other problems associated with the prior art.
The present invention is a torque producing apparatus comprising first and second members and retention means. The first member has a first arm, a second arm, and a connection portion. The first and second arms have an inner and an outer surface and define an aperture. The first and second arms have an opening between the inner and outer surfaces. When the member is in a relaxed state, at least one of the inner or the outer surface has a predetermined diameter. The second member has a surface that engages one of the inner or outer surface of the first member. The retention means engages the connection portion of the first member so that the second member rotates relative to the first member upon relative rotation of the second member and the retention means.
In one embodiment of the present invention the second member is a rotatable shaft. The shaft has a surface with an outer diameter greater than a predetermined diameter of the inner surface of the first member when the first member is in a relaxed state. The surface of the shaft is engaged in interference fit to the inner surface of the first member. The retention means engages the connection portion of the first member so that the shaft rotates relative to the first member upon relative rotation of the shaft and the retention means.
In another embodiment of the present invention the second member is a sleeve. The sleeve has a surface with an inner diameter smaller than a predetermined diameter of the outer surface of the first member when the first member is in a relaxed state. The surface of the sleeve is engaged in interference fit to the outer surface of the first member. The retention means includes a shaft configured to engage the connection portion of the first member so that the sleeve rotates relative to the first member upon relative rotation of the sleeve and the shaft.